On the 11th of November 2003 the Korean players
Cho HunHyun and Lee ChangHo wrote a piece of Go history
by creating a new opening pattern at as early as move 3.
Up to that day the position after black 'A' in the
diagram below had never been played before
at professional level.

The likely reason why 'A' in the diagram has never
been played before is that occupying the upper-left
corner makes more sense considering the high positions
of black 1 and white 2 towards that corner while these
stones have a low (uninteresting) position towards the
lower-right corner. Lee ChangHo decided to play 'A'
anyway and went on to win the game. This is a fine
example of the freedom of choice Go players have in
deciding their opening moves.